In a variety of subsea applications, fluids are directed from one locale to another. Depending on the activity, fluid may be directed through subsea flowlines located on the seafloor or directed upwardly from a subsea well, pipe, vessel, or other container to the water surface. Typically, subsea pumps are used to direct subsea fluids from one locale to another. In one known subsea pumping technique, hydraulic drive systems have been employed for powering subsea pumps. However, the motor powering the pump may have to overcome a given hydrostatic pressure when returning motor fluids back to the water surface, the result may include a time intensive endeavor placing an unwanted load on the motor powering the subsea pump. In another known subsea pumping technique, electric drive systems have been employed to power subsea pumps. However, at great depths it may be difficult to supply the necessary current and amperage to effectively pump fluids to the water surface from great depths.
A more efficient technique for transporting subsea fluid is desired.
In petroleum production, oil and its byproducts are typically removed from wells and transported through pipelines, including subsea pipelines. The flow of oil and other fluids through a subsea pipeline can lead to the build up of different substances within the pipe impeding fluid flow there through. For example, scale, paraffin wax, gas hydrates, debris or sand may buildup in the pipeline over time depending on the nature of the fluid flowing through the pipeline and other surrounding circumstances.
One method to prevent the formation of paraffin deposits is to heat the pipelines. However, this method is very expensive and is not feasible for subsea pipelines submerged in the cold sea water. Another method involves “pigging”, wherein a mechanical device is passed through the pipeline scraping the inner wall of the pipeline and pushing paraffin deposits through. Another method for removing paraffin deposits is “hot oiling,” wherein a heated oil is pumped through the pipeline in order to remove the paraffin wax deposits.
Another cause of blockage in subsea pipelines is the formation of gas hydrates where an aqueous phase is inherently present, during the transportation of fluids including gases. This is a common problem, especially in deep sea conditions including low temperatures. Low temperatures and the presence of water lead to formation of gas hydrates in the pipelines.
One method of dealing with gas hydrates is to insulate the pipeline. But, this approach is typically expensive. Another method is to pump methanol through the pipeline or use chemical methods such as addition of anti-agglomerates (e.g. kinetic inhibitors or thermodynamic inhibitors). However, to be effective, large quantities of these chemicals are required making the process expensive.